U.S. patent application number 15/647354 was filed with the patent office on 2018-09-20 for thermal air flow meter.
This patent application is currently assigned to Mitsubishi Electric Corporation. The applicant listed for this patent is Mitsubishi Electric Corporation. Invention is credited to Yuji ARIYOSHI, Shinichiro HIDAKA, Masahiro KAWAI, Naoki MORINAGA.
Application Number | 20180266861 15/647354 |
Document ID | / |
Family ID | 61968273 |
Filed Date | 2018-09-20 |
United States Patent
Application |
20180266861 |
Kind Code |
A1 |
MORINAGA; Naoki ; et
al. |
September 20, 2018 |
THERMAL AIR FLOW METER
Abstract
This signal processing unit includes: a comparison signal output
unit which outputs a comparison signal on a negative side that
corresponds to a negative side portion, of a second
amplitude-increased signal, which is on the negative side with
respect to the comparison threshold TH; an averaging processing
unit which outputs an average signal obtained by averaging the
comparison signal; a coefficient multiplication processing unit
which outputs a coefficient-multiplied signal obtained by
multiplying the average signal by an adjustment coefficient set in
advance; and a signal correction processing unit which outputs, as
a flow rate signal, a value obtained by correcting a first
amplitude-increased signal so as to be decreased by use of the
coefficient-multiplied signal, wherein the comparison threshold TH
is set on the basis of an output characteristic of a sensor
measured in advance with respect to at least a forward flow
direction of an intake air.
Inventors: |
MORINAGA; Naoki; (Tokyo,
JP) ; ARIYOSHI; Yuji; (Tokyo, JP) ; HIDAKA;
Shinichiro; (Tokyo, JP) ; KAWAI; Masahiro;
(Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Electric Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Mitsubishi Electric
Corporation
Tokyo
JP
|
Family ID: |
61968273 |
Appl. No.: |
15/647354 |
Filed: |
July 12, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02D 41/24 20130101;
G01F 1/69 20130101; F02D 41/18 20130101; F02D 41/26 20130101; F02D
41/187 20130101; F02D 41/28 20130101; F02M 35/10386 20130101; F02D
2041/285 20130101; G01F 1/692 20130101; G01F 1/698 20130101; G01F
1/6842 20130101; G01F 5/00 20130101; G01F 5/005 20130101; G01F 1/72
20130101 |
International
Class: |
G01F 1/692 20060101
G01F001/692; G01F 1/698 20060101 G01F001/698; G01F 1/72 20060101
G01F001/72; G01F 1/684 20060101 G01F001/684; G01F 5/00 20060101
G01F005/00; F02D 41/18 20060101 F02D041/18 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 15, 2017 |
JP |
2017-049340 |
Claims
1. A thermal air flow meter comprising: a bypass flow path which is
disposed in an intake pipe in which intake air to be taken into an
internal combustion engine flows, and which takes in part of the
intake air and causes the part of the intake air to flow
therethrough; a sensor which has a flow rate detection element
disposed in the bypass flow path and which outputs an output signal
that corresponds to a flow rate of the intake air flowing in a
forward flow direction and a reverse flow direction in the intake
pipe; and a signal processing unit which processes the output
signal of the sensor, wherein the signal processing unit includes
following processing: outputting a first amplitude-increased signal
and a second amplitude-increased signal which are each obtained by
subjecting the output signal of the sensor to an
amplitude-increasing process of an alternating current component
thereof; comparing the second amplitude-increased signal with a
comparison threshold set in advance, and which outputs a comparison
signal on a negative side that corresponds to a negative side
portion, of the second amplitude-increased signal, which is on the
negative side with respect to the comparison threshold; outputting
an average signal obtained by averaging the comparison signal;
outputting a coefficient-multiplied signal obtained by multiplying
the average signal by an adjustment coefficient set in advance; and
outputting, as a flow rate signal, a value obtained by correcting
the first amplitude-increased signal so as to be decreased by use
of the coefficient-multiplied signal, and the comparison threshold
is set on the basis of an output characteristic of the sensor
measured in advance.
2. The thermal air flow meter according to claim 1, wherein the
comparison threshold is set on the basis of a flow rate
characteristic on the reverse flow side as the output
characteristic of the sensor.
3. The thermal air flow meter according to claim 1, wherein the
comparison threshold is set by an approximate expression obtained
through calculation of the flow rate signal at at least two flow
rate points on the forward flow side in the output characteristic
of the sensor.
4. The thermal air flow meter according to claim 1, wherein the
comparison threshold is set by an approximate expression calculated
from an output at a time of no air flow and an output at one flow
rate point in a forward flow side characteristic in the output
characteristic of the sensor.
5. The thermal air flow meter according to claim 1, wherein the
sensor includes, as the flow rate detection element, an upstream
heating resistor disposed to an upstream side of the intake air,
and a downstream heating resistor disposed to a downstream side of
the intake air with respect to the upstream heating resistor.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to a thermal air flow meter
which detects the flow rate of intake air in an internal combustion
engine.
2. Description of the Background Art
[0002] Thermal air flow meters capable of measuring the mass flow
rate of intake air have been widely used in
electronically-controlled fuel injection systems for internal
combustion engines mounted in vehicles or the like.
[0003] However, in such a thermal air flow meter, a pulsation flow
accompanied with a reverse flow occurs under an operation condition
of a low rotation rate and a high load of an internal combustion
engine.
[0004] Thus, in a conventional thermal air flow meter that cannot
detect a reverse flow, a large flow rate detection error
occurs.
[0005] In order to reduce such a flow rate detection error during
measurement of a pulsation flow accompanied with a reverse flow, a
method has been proposed in which: an air flow direction is
detected; and when a reverse flow has been detected, a flow rate
signal is corrected.
[0006] For example, in the technology according to Japanese Patent
No. 5558599, when a pulsation accompanied with a reverse flow has
occurred, a differential amplifier unit 2 takes out a flow rate
signal in the reverse flow direction and the flow rate signal is
converted into a pulse signal. Then, this pulse signal is smoothed
by an LPF unit, and the resultant signal is subtracted from the
original flow rate signal, whereby pulsation correction is
performed.
[0007] However, there is no description of a method for setting a
reference voltage that is used when the differential amplifier unit
2 takes out a flow rate signal Vd1 in the reverse flow direction,
and variation in other electronic components influences the
reference voltage at the time of the flow rate signal in the
reverse flow direction being taken out. This causes a problem of
increased variation in pulsation characteristics in individual
sensors.
SUMMARY OF THE INVENTION
[0008] The present invention has been made in order to solve the
above-described problem in conventional technologies. An object of
the present invention is to provide a thermal air flow meter that
can realize accurate flow rate measurement by means of inexpensive
configuration, even when a pulsation flow accompanied with a
reverse flow has occurred.
[0009] The present invention is a thermal air flow meter including:
a bypass flow path which is disposed in an intake pipe in which
intake air to be taken into an internal combustion engine flows,
and which takes in part of the intake air and causes the part of
the intake air to flow therethrough; a sensor which has a flow rate
detection element disposed in the bypass flow path and which
outputs an output signal that corresponds to a flow rate of the
intake air flowing in a forward flow direction and a reverse flow
direction in the intake pipe; and a signal processing unit which
processes the output signal of the sensor, wherein the signal
processing unit includes: a response correction unit which outputs
a first amplitude-increased signal and a second amplitude-increased
signal which are each obtained by subjecting the output signal of
the sensor to an amplitude-increasing process of an alternating
current component thereof; a comparison signal output unit which
compares the second amplitude-increased signal with a comparison
threshold set in advance, and which outputs a comparison signal on
a negative side that corresponds to a negative side portion, of the
second amplitude-increased signal, which is on the negative side
with respect to the comparison threshold; an averaging processing
unit which outputs an average signal obtained by averaging the
comparison signal; a coefficient multiplication processing unit
which outputs a coefficient-multiplied signal obtained by
multiplying the average signal by an adjustment coefficient set in
advance; and a signal correction processing unit which outputs, as
a flow rate signal, a value obtained by correcting the first
amplitude-increased signal so as to be decreased by use of the
coefficient-multiplied signal, and the comparison threshold is set
on the basis of an output characteristic of the sensor measured in
advance.
[0010] According to the present invention, a comparison threshold
that could influence pulsation correction can be accurately set in
individual sensors. In addition, even when the reverse flow
characteristic is not measured, a comparison threshold can be
accurately set. Thus, capital investment for measuring the reverse
flow characteristic is not required, and man-hour at the time of
assembling can be reduced.
[0011] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description when read in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a side sectional view of a thermal air flow meter
according to a first embodiment of the present invention, cut along
a plane parallel to a flow direction X of intake air;
[0013] FIG. 2 is a plan view of a flow rate detection element of
the thermal air flow meter according to the first embodiment of the
present invention;
[0014] FIG. 3 is a cross-sectional view of the flow rate detection
element cut along the A-A line in FIG. 2;
[0015] FIG. 4 is a circuit diagram of a sensor and a block diagram
of a signal processing unit of the thermal air flow meter according
to the first embodiment of the present invention;
[0016] FIG. 5 shows an output characteristic of the sensor
according to the first embodiment of the present invention;
[0017] FIG. 6 is an operation waveform chart describing a mechanism
of how a flow rate detection error occurs when a pulsation flow
accompanied with a reverse flow has occurred;
[0018] FIG. 7 is an operation waveform chart describing a
comparison example where processing different from that in the
first embodiment of the present invention is performed;
[0019] FIGS. 8A and 8B are an explanation diagram showing a
pulsation error in the comparison example shown in FIG. 7;
[0020] FIGS. 9A to 91 show operation waveforms according to the
first embodiment of the present invention;
[0021] FIG. 10 is an explanation diagram showing a pulsation error
in the first embodiment of the present invention;
[0022] FIG. 11 is a diagram describing setting of comparison
thresholds for the signal processing unit in the first embodiment
of the present invention; and
[0023] FIG. 12 shows pulsation error when the comparison thresholds
are set at the upper limit value, the median, and the lower limit
value of variation in a second embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
First Embodiment
[0024] A thermal air flow meter 1 according to the present
embodiment is described with reference to the drawings.
[0025] The thermal air flow meter 1 is mounted to an intake pipe 35
in which intake air to be taken into an internal combustion engine
flows.
[0026] FIG. 1 is a side sectional view of the thermal air flow
meter 1 mounted to the intake pipe 35, cut along a plane parallel
to a flow direction X of intake air.
[0027] In a state where a main unit 26 of the thermal air flow
meter 1 is inserted in the intake pipe 35 through an insertion hole
36 provided in the intake pipe 35, a flange portion 30 of the
thermal air flow meter 1 is fixed to the intake pipe 35.
[0028] The thermal air flow meter 1 includes: a bypass flow path 29
which is disposed in the intake pipe 35 and which takes in part of
intake air flowing in the intake pipe 35 and causes the part of the
intake air to flow therethrough; a sensor 25 having a flow rate
detection element 24 disposed in the bypass flow path 29; and a
signal processing unit 3 which processes an output signal Vm of the
sensor 25.
[0029] In the main unit 26, a connector portion 33, a circuit
housing portion 27, and the bypass flow path 29 are formed along
the insertion direction of the main unit 26 into the intake pipe 35
of the thermal air flow meter 1.
[0030] The circuit housing portion 27 houses a circuit board 28 on
which a differential current output circuit 18 of the sensor 25 and
a processing circuit of the signal processing unit 3 described
later are mounted.
[0031] A drive power supply 22 for each circuit and a flow rate
signal Vout from the signal processing unit 3 are connected, via
the connector portion 33, to an external power supply and an
external control device.
[0032] <Bypass Flow Path 29>
[0033] Intake air in the intake pipe 35 usually flows in a forward
flow direction X1 during operation of the internal combustion
engine.
[0034] The forward flow direction X1 is the direction of flow
advancing from the inlet of the intake pipe 35 toward the internal
combustion engine.
[0035] However, when a throttle valve provided in the intake pipe
35 to the downstream side in the forward flow direction X1 relative
to the thermal air flow meter 1 is opened, and the differential
pressure between the upstream and the downstream of the throttle
valve decreases, a pressure pulsation is transmitted to the thermal
air flow meter 1 from the internal combustion engine side.
[0036] Due to this pressure pulsation, the flow rate of the intake
air flowing in the vicinity of the thermal air flow meter 1 is
pulsated.
[0037] When the amplitude of the transmitted pressure pulsation
increases, a section in which the intake air flows in a reverse
flow direction X2 occurs in the pulsation flow.
[0038] The reverse flow direction X2 is the direction of flow
advancing from the internal combustion engine toward the inlet of
the intake pipe 35.
[0039] Thus, the intake air in the intake pipe 35 flows not only in
the forward flow direction X1 but also in the reverse flow
direction X2 under the influence of pulsation.
[0040] Meanwhile, the bypass flow path 29 is configured to allow
air to pass therethrough in a direction according to the forward
flow direction X1 or the reverse flow direction X2 of the intake
air in the intake pipe 35.
[0041] That is, when the intake air is flowing in the forward flow
direction X1 within the intake pipe 35, air flows in the forward
flow direction X1 within the bypass flow path 29.
[0042] Meanwhile, when the intake air is flowing in the reverse
flow direction X2 within the intake pipe 35, air flows in the
reverse flow direction X2 within the bypass flow path 29.
[0043] In the present embodiment, the bypass flow path 29 includes:
a flow-in hole 31 which is open toward the upstream side of the
forward flow direction X1; and a flow-out hole 32 which is open
toward a direction perpendicular to the flow direction X (in the
present example, the insertion direction of the main unit 26).
[0044] Part of the intake air flowing in the forward flow direction
X1 flows into the flow-in hole 31, flows in the forward flow
direction X1 within the bypass flow path 29, passes the flow rate
detection element 24, and then, flows through the flow-out hole 32
into the intake pipe 35.
[0045] Meanwhile, part of the intake air flowing in the reverse
flow direction X2 flows into the flow-out hole 32, flows in the
reverse flow direction X2 within the bypass flow path 29, passes
the flow rate detection element 24, and then, flows through the
flow-in hole 31 into the intake pipe 35.
[0046] The flow-out hole 32 is open in the direction perpendicular
to the flow direction X. Therefore, under a condition in which the
flow rates of the intake air in the forward flow direction X1 and
in the reverse flow direction X2 are the same, the flow rate of the
intake air in the reverse flow direction X2 flowing into the
flow-out hole 32 is less than the flow rate of the intake air in
the forward flow direction X1 flowing into the flow-in hole 31.
[0047] In the present embodiment, the bypass flow path 29 is
provided with a sub flow-out hole 37, but may not be provided with
the sub flow-out hole 37.
[0048] <Sensor 25>
[0049] The sensor 25 has the flow rate detection element 24
disposed in the bypass flow path 29.
[0050] FIG. 2 is a plan view of the flow rate detection element
24.
[0051] FIG. 3 is a cross-sectional view of the flow rate detection
element 24 cut along the A-A line in FIG. 2.
[0052] The sensor 25 includes, as the flow rate detection element
24: an upstream heating resistor 181 which is a heating resistor at
the upstream side in the forward flow direction X1; and a
downstream heating resistor 182 which is a heating resistor
disposed to the downstream side in the forward flow direction X1
relative to the upstream heating resistor 181.
[0053] When air flows in the forward flow direction X1, the
temperature of the upstream heating resistor 181 becomes low
relative to that of the downstream heating resistor 182.
[0054] When air flows in the reverse flow direction X2, the
temperature of the downstream heating resistor 182 becomes low
relative to that of the upstream heating resistor 181.
[0055] In addition, the relative temperature difference increases
in accordance with increase in the flow rate in the forward flow
direction X1 or in the reverse flow direction X2.
[0056] The resistance value of the heating resistor 181, 182
decreases in accordance with decrease in the temperature
thereof.
[0057] Although details are described later, by using the
resistance difference caused by the relative temperature
difference, the flow direction and the magnitude of the flow rate
can be detected.
[0058] The flow rate detection element 24 is composed of a silicon
substrate 241 and an insulation film 242 formed on a surface
thereof. The upstream heating resistor 181 and the downstream
heating resistor 182 are formed in the insulation film 242.
[0059] The silicon substrate 241 on the back surface side of the
portion of the insulation film 242 where the heating resistors 181
and 182 are formed has been removed through etching or the like. As
a result, the portion where the heating resistors 181 and 182 are
formed is in the form of a thin film.
[0060] FIG. 4 is a circuit diagram of the sensor 25 and a block
diagram of the signal processing unit 3.
[0061] The sensor 25 includes the differential current output
circuit 18. The differential current output circuit 18 generates
the output signal Vm which corresponds to the difference between:
an upstream current Ihu which flows in the upstream heating
resistor 181 in order to keep the voltage across both ends of the
upstream heating resistor 181 at an upstream voltage value set in
advance; and a downstream current Ihd which flows in the downstream
heating resistor 182 in order to keep the voltage across both ends
of the downstream heating resistor 182 at a downstream voltage
value set in advance.
[0062] In the present embodiment, the differential current output
circuit 18 includes an upstream fixed resistance 20, a downstream
fixed resistance 19, an operational amplifier 23, and an output
resistance 21.
[0063] The output terminal of the operational amplifier 23 and the
negative-side input terminal of the operational amplifier 23 are
connected to each other via the output resistance 21.
[0064] This connection forms a negative feedback circuit in which
when a potential difference has occurred between the negative-side
input terminal and the positive-side input terminal of the
operational amplifier 23, current flows in the output resistance 21
so as to eliminate the potential difference.
[0065] The downstream fixed resistance 19 and the upstream fixed
resistance 20 are connected in series in this order, between the
power supply 22 and the ground.
[0066] The connection portion between the downstream fixed
resistance 19 and the upstream fixed resistance 20 is connected to
the positive-side input terminal of the operational amplifier
23.
[0067] Thus, a voltage obtained by a power supply voltage Vc being
divided between the downstream fixed resistance 19 and the upstream
fixed resistance 20 is inputted to the positive-side input terminal
of the operational amplifier 23.
[0068] The voltage across both ends of the upstream fixed
resistance 20, which is a divided power supply voltage Vc,
corresponds to the upstream voltage value. The voltage across both
ends of the downstream fixed resistance 19, which is the other
divided power supply voltage Vc, corresponds to the downstream
voltage value.
[0069] In the present embodiment, the upstream fixed resistance 20
and the downstream fixed resistance 19 have the same resistance
value R, the upstream voltage value and the downstream voltage
value are each 1/2 of the power supply voltage Vc, and 1/2 of the
power supply voltage Vc is inputted to the positive-side input
terminal of the operational amplifier 23.
[0070] The downstream heating resistor 182 and the upstream heating
resistor 181 are connected in series in this order, between the
power supply 22 and the ground.
[0071] The connection portion between the downstream heating
resistor 182 and the upstream heating resistor 181 is connected to
the negative-side input terminal of the operational amplifier
23.
[0072] Thus, a voltage Vh obtained by the power supply voltage Vc
being divided between the downstream heating resistor 182 and the
upstream heating resistor 181 is inputted to the negative-side
input terminal of the operational amplifier 23.
[0073] In the present embodiment, the downstream heating resistor
182 and the upstream heating resistor 181 have the same resistance
value if the temperatures thereof are the same.
[0074] In a case where the flow is in the forward flow direction
X1, the temperature of the upstream heating resistor 181 is lowered
relative to that of the downstream heating resistor 182. Thus, the
resistance value of the upstream heating resistor 181 is lowered
relative to that of the downstream heating resistor 182.
[0075] As a result, the voltage Vh at the negative-side input
terminal of the operational amplifier 23 becomes lower than the
voltage (Vc/2) at the positive-side input terminal of the
operational amplifier 23.
[0076] Accordingly, the voltage Vm at the output terminal of the
operational amplifier 23 becomes higher than the voltage Vh at the
negative-side input terminal thereof, and a current Im flows in the
output resistance 21 from the output terminal side toward the
negative-side input terminal side.
[0077] The upstream current Ihu flowing in the upstream heating
resistor 181 becomes larger than the downstream current Ihd flowing
in the downstream heating resistor 182.
[0078] The current Im flowing in the output resistance 21 is
expressed as Expression (1).
[0079] In accordance with increase in the flow rate in the forward
flow direction X1, the relative amount of decrease in temperature
and the relative amount of decrease in resistance of the upstream
heating resistor 181 increase. Thus, the current Im increases.
Ihu>Ihd
Im=Ihu-Ihd>0 (1)
[0080] Meanwhile, in a case where the flow is in the reverse flow
direction X2, the temperature of the downstream heating resistor
182 is lowered relative to that of the upstream heating resistor
181. Thus, the resistance value of the downstream heating resistor
182 is lowered relative to that of the upstream heating resistor
181.
[0081] As a result, the voltage Vh at the negative-side input
terminal of the operational amplifier 23 becomes higher than the
voltage (Vc/2) at the positive-side input terminal of the
operational amplifier 23.
[0082] Accordingly, the voltage Vm at the output terminal of the
operational amplifier 23 becomes lower than the voltage Vh at the
negative-side input terminal thereof, and the current Im flows in
the output resistance 21 from the negative-side input terminal side
toward the output terminal side.
[0083] The downstream current Ihd flowing in the downstream heating
resistor 182 becomes larger than the upstream current Ihu flowing
in the upstream heating resistor 181.
[0084] The current Im is expressed as Expression (2).
[0085] In accordance with increase in the flow rate in the reverse
flow direction X2, the relative amount of decrease in temperature
and the relative amount of decrease in resistance of the downstream
heating resistor 182 increase. Thus, the current Im decreases.
Ihu<Ihd
Im=Ihu-Ihd<0 (2)
[0086] The voltage Vm at the output terminal of the operational
amplifier 23, that is, the output signal Vm of the sensor 25 is
expressed as Expression (3).
[0087] Here, Rm is the resistance value of the output resistance
21.
[0088] Thus, as shown in FIG. 5, the output signal Vm of the sensor
25 exhibits a characteristic in which the output signal Vm
monotonically increases in accordance with increase in the flow
rate, both in the forward flow and the reverse flow.
Vm=Vc/2+Rm.times.Im (3)
[0089] FIG. 5 shows the output characteristic of the sensor 25
according to the present embodiment.
[0090] The flow rate in the forward flow direction X1 is expressed
by positive values, and the flow rate in the reverse flow direction
X2 is expressed by negative values.
[0091] That is, in accordance with increase in the magnitude of the
flow rate in the forward flow direction X1, the flow rate increases
from 0 (zero), and in accordance with increase in the magnitude of
the flow rate in the reverse flow direction X2, the flow rate
decreases from 0.
[0092] The output characteristic of the sensor 25 is a nonlinear
monotonically increasing characteristic.
[0093] In addition, the output characteristic of the sensor 25 is
different between the forward flow direction X1 side where the flow
rate is greater than 0 and the reverse flow direction X2 side where
the flow rate is smaller than 0.
[0094] Specifically, on the forward flow direction X1 side, the
output characteristic of the sensor 25 is: as the flow rate
increases from 0, the slope of the increase in the output signal Vm
against the increase in the flow rate decreases, accordingly.
[0095] On the reverse flow direction X2 side, the output
characteristic of the sensor 25 is: as the flow rate decreases from
0, the slope of the decrease in the output signal Vm against the
decrease in the flow rate decreases, accordingly.
[0096] In addition, due to the difference and the like in the
directions in which the flow-in hole 31 and the flow-out hole 32 of
the bypass flow path 29 are open, if the magnitude of the flow rate
of the intake air in the forward flow direction X1 and the
magnitude of the flow rate of the intake air in the reverse flow
direction X2 are the same, the output sensitivity to the flow rate
in the reverse flow direction X2 is lower than that in the forward
flow direction X1.
[0097] That is, the slope of the output signal Vm against the flow
rate in the reverse flow direction X2 is smaller than that in the
forward flow direction X1.
[0098] When the temperature of the heating resistor 181, 182
changes in response to change in the flow rate, there is response
delay due to the heat capacity or the like of the heating
resistor.
[0099] Thus, there is response delay in the output signal Vm of the
sensor 25, relative to the true flow rate.
[0100] When a pulsation flow has occurred, an amplitude of the
pulsation flow that corresponds to the output signal Vm of the
sensor 25 is decreased relative to the true amplitude of the
pulsation flow.
[0101] <Signal Processing Unit 3>
[0102] The signal processing unit 3 processes the output signal Vm
of the sensor 25, and outputs the flow rate signal Vout. As shown
in FIG. 4, the signal processing unit 3 includes a response
correction unit 7, a comparison signal output unit 8, an averaging
processing unit 9, a coefficient multiplication processing unit 10,
and a signal correction processing unit 11.
[0103] Each processing unit 7 to 11 of the signal processing unit 3
is realized by a processing circuit.
[0104] In the present embodiment, the signal processing unit 3 is
composed of a digital processing circuit.
[0105] Specifically, the signal processing unit 3 includes: an
arithmetic processing unit such as a DSP (digital signal
processor); a storage device which communicates data with the
arithmetic processing unit; an A/D converter (analog-digital
converter) which inputs the output signal Vm of the sensor 25 to
the arithmetic processing unit; a D/A converter (digital-analog
converter) which outputs to the outside the flow rate signal Vout
processed by the arithmetic processing unit; and the like.
[0106] Each function of the processing unit 7 to 11 of the signal
processing unit 3 is realized by the arithmetic processing unit
executing programs stored in the storage device and by the
arithmetic processing unit cooperating with the storage device, the
A/D converter, the D/A converter, and the like.
[0107] The data of settings such as a comparison threshold TH used
by each processing unit 7 to 11 or the like is stored in the
storage device, as a part of a program.
[0108] The mechanism of how a flow rate detection error occurs when
a pulsation flow accompanied with a reverse flow has occurred is
described.
[0109] In a case of a sensor that cannot detect a reverse flow
according to a comparison example, which is different from the
present embodiment, as shown in the upper right graph in FIG. 6, in
a reverse flow occurrence region, the output signal of the sensor
is higher than the output at a time of no air flow. Thus, if the
output signal of the sensor is directly converted into a flow rate,
the waveform will have a shape in which the portion of the waveform
at the time of occurrence of a reverse flow is folded to the
forward flow side.
[0110] The detected average flow rate of 1 cycle of pulsation,
which is important for control of the internal combustion engine,
becomes larger than the true average flow rate, and thus, a
detection error (hereinafter, referred to as pulsation error)
occurs.
[0111] In a case of a comparison example where processing different
from that in the present embodiment is performed, even when the
sensor 25 capable of detecting a reverse flow as in the present
embodiment is used, a pulsation error occurs, as shown in FIG. 7,
in which the detected average flow rate detected on the basis of
the output signal Vm of the sensor 25 is shifted to the positive
side with respect to the true average flow rate, due to the
nonlinear output characteristic of the sensor 25 and the response
delay of the output signal Vm described above.
[0112] The reason for this is as follows. As described above, in
the reverse flow occurrence region, in accordance with increase in
the magnitude of the reverse flow rate, the slope of the output
signal Vm against the flow rate decreases, and thus, the
sensitivity of the output signal Vm to the increase in the
magnitude of the reverse flow rate is reduced.
[0113] In addition, due to the difference in the directions in
which the flow-in hole 31 and the flow-out hole 32 of the bypass
flow path 29 are open, the sensitivity of the output signal Vm to
the reverse flow rate is made lower.
[0114] Thus, when assuming that there is no response delay, the
sensitivity of the output signal Vm to the increase in the
magnitude of the reverse flow rate is reduced, and when there is
response delay, the output signal Vm is shifted to the forward flow
rate side (positive side) where the sensitivity is high.
[0115] Thus, the detected average flow rate detected on the basis
of the output signal Vm having response delay is shifted to the
positive side with respect to the true average flow rate.
[0116] In the case of this comparison example, as shown in FIGS. 8A
and 8B, where the horizontal axis represents amplitude ratio and
the vertical axis represents pulsation error, in a reverse flow
occurrence region where the amplitude ratio is larger than 1, the
pulsation error accordingly increases toward the positive side as
the amplitude ratio becomes larger than 1.
[0117] Here, the amplitude ratio is the ratio of the amplitude Qamp
of the pulsation flow relative to the average flow rate Qave of the
pulsation flow (=Qamp/Qave). The pulsation error is the ratio of
the detected average flow rate relative to the true average flow
rate (=detected average flow rate/true average flow rate-1).
[0118] Thus, in the present embodiment, as described below, in
order to reduce the amount of the shift on the positive side of the
detected average flow rate when a pulsation flow accompanied with a
reverse flow has occurred, decrease correction which decreases the
flow rate signal Vout is performed.
[0119] That is, the response correction unit 7 outputs an
amplitude-increased signal which is obtained by subjecting the
output signal Vm of the sensor 25 to an amplitude-increasing
process of an alternating current component thereof.
[0120] The comparison signal output unit 8 compares the
amplitude-increased signal with a comparison threshold TH set in
advance, and outputs a comparison signal Vfc on the negative side
that corresponds to a negative side portion, of the
amplitude-increased signal, which is on the negative side with
respect to the comparison threshold TH.
[0121] The averaging processing unit 9 outputs an average signal
Vfca obtained by averaging the comparison signal Vfc.
[0122] The coefficient multiplication processing unit 10 outputs a
coefficient-multiplied signal Vfk obtained by multiplying the
average signal Vfca by an adjustment coefficient Kad set in
advance.
[0123] The signal correction processing unit 11 outputs, as the
flow rate signal Vout, a value obtained by correcting the
amplitude-increased signal so as to be decreased by use of the
coefficient-multiplied signal Vfk.
[0124] Due to response delay of the sensor 25, with respect to the
output signal Vm, the amplitude of the alternating current
component of the pulsation flow has been decreased.
[0125] By the response correction unit 7, the amplitude of the
alternating current component of the output signal Vm can be
increased, whereby influence of the response delay of the sensor 25
can be reduced.
[0126] However, merely by performing the amplitude-increasing
process of the alternating current component, the shift on the
positive side of the detected average flow rate cannot be
eliminated.
[0127] Thus, by outputting the comparison signal Vfc on the
negative side that corresponds to a negative side portion, of the
amplitude-increased signal, which is on the negative side with
respect to the comparison threshold TH, a component that
corresponds to the reverse flow rate can be extracted.
[0128] By outputting the average signal Vfca obtained by averaging
the comparison signal Vfc, a signal that corresponds to the average
value of the reverse flow rate can be outputted.
[0129] By outputting the coefficient-multiplied signal Vfk obtained
by multiplying the average signal Vfca by the adjustment
coefficient Kad, a signal corresponding to the amount of the shift
on the positive side of the detected average flow rate and having
occurred due to the reverse flow rate can be outputted.
[0130] Then, by outputting, as the flow rate signal Vout, a value
obtained by correcting the amplitude-increased signal so as to be
decreased by use of the coefficient-multiplied signal Vfk, the
amount of the shift on the positive side of the detected average
flow rate and having occurred due to the reverse flow rate can be
reduced.
[0131] In the present embodiment, as shown in FIG. 4, the response
correction unit 7 outputs a first amplitude-increased signal Vf1
obtained by subjecting the output signal Vm of the sensor 25 to a
first amplitude-increasing process of an alternating current
component thereof, and outputs a second amplitude-increased signal
Vf2 obtained by subjecting the output signal Vm of the sensor 25 to
a second amplitude-increasing process of the alternating current
component.
[0132] Then, the comparison signal output unit 8 compares the
second amplitude-increased signal Vf2 with the comparison threshold
TH, and outputs the comparison signal Vfc on the negative side.
[0133] The signal correction processing unit 11 outputs, as the
flow rate signal Vout, a value obtained by correcting the first
amplitude-increased signal Vf1 so as to be decreased by use of the
coefficient-multiplied signal Vfk.
[0134] According to this configuration, two amplitude-increasing
processes are performed. Thus, it is possible to perform the first
amplitude-increasing process that is suitable for outputting the
first amplitude-increased signal Vf1 which serves as the base
signal for the flow rate signal Vout, and to perform the second
amplitude-increasing process that is suitable for the process of
reducing the amount of the shift.
[0135] That is, it is possible to perform amplitude-increasing
processes that are suitable for the respective objectives of the
response correction and the shift correction, and it is possible to
improve the processing accuracy of the flow rate signal Vout.
[0136] FIGS. 9A to 91 show operation waveforms according to the
present embodiment.
[0137] In a case where a pulsation flow accompanied with a reverse
flow as shown in FIG. 9A has occurred, the output signal Vm of the
sensor 25 having been subjected to A/D conversion becomes as shown
in FIG. 9B.
[0138] In the output signal Vm of the sensor 25, the amplitude of
the alternating current component has decreased due to response
delay.
[0139] With respect to the first amplitude-increased signal Vf1
shown in FIG. 9C, the amplitude of the alternating current
component has been increased than in the output signal Vm, as a
result of the first amplitude-increasing process performed by the
response correction unit 7.
[0140] With respect to the second amplitude-increased signal Vf2
shown in FIG. 9D, the amplitude of the alternating current
component has been increased than in the output signal Vm, as a
result of the second amplitude-increasing process performed by the
response correction unit 7.
[0141] For each amplitude-increasing process, a response advancing
process or the like is used which is an inverse characteristic to
the response delay characteristic of the sensor 25.
[0142] The set constants of the response advancing processes are
set to different values, in accordance with respective objectives
of the first amplitude-increasing process and the second
amplitude-increasing process.
[0143] In the present embodiment, as shown in FIGS. 9D, 9E, and 9F,
and Expression (4), the comparison signal output unit 8 compares
the second amplitude-increased signal Vf2 with the comparison
threshold TH, and extracts a negative side portion, of the second
amplitude-increased signal Vf2, which is on the negative side with
respect to the comparison threshold TH.
[0144] Then, when there is a negative side portion, of the second
amplitude-increased signal Vf2, which is on the negative side with
respect to the comparison threshold TH, the comparison signal
output unit 8 outputs the absolute value of the negative side
portion of the second amplitude-increased signal Vf2, as the
comparison signal Vfc on the negative side.
[0145] When there is no negative side portion of the second
amplitude-increased signal Vf2, the comparison signal output unit 8
outputs 0 as the comparison signal Vfc on the negative side.
[0146] In accordance with increase in the reverse flow rate, the
comparison signal Vfc on the negative side increases.
[0147] 1) When Vf2<TH
Vfc=|Vf2-TH| (4)
[0148] 2) When Vf2.gtoreq.TH
Vfc=0
[0149] As shown in FIG. 9G, the averaging processing unit 9 outputs
the average signal Vfca obtained by averaging the comparison signal
Vfc.
[0150] The averaging process is performed by use of a
moving-average process, a lowpass filter process, or the like.
[0151] As shown in FIG. 9H and Expression (5), the coefficient
multiplication processing unit 10 outputs, as the
coefficient-multiplied signal Vfk, a value obtained by multiplying
the average signal Vfca by the adjustment coefficient Kad.
Vfk=Kad.times.Vfc (5)
[0152] As shown in FIGS. 9A to 91, the signal correction processing
unit 11 outputs, as the flow rate signal Vout, a value obtained by
subtracting the coefficient-multiplied signal Vfk, which has a
positive value, from the first amplitude-increased signal Vf1.
[0153] The detected average flow rate calculated from the flow rate
signal Vout can be made close to the true average flow rate.
[0154] Since the coefficient-multiplied signal Vfk increases in
accordance with increase in the reverse flow rate, the amount of
the shift on the positive side which increases in accordance with
increase in the reverse flow rate can be appropriately reduced.
[0155] As a result, as shown in FIG. 10, the pulsation error can be
reduced in a reverse flow occurrence region where the amplitude
ratio becomes larger than 1.
[0156] However, with respect to the comparison threshold TH used by
the comparison signal output unit 8 described above, the comparison
thresholds TH set for the individual sensors are different,
respectively, because the reverse flow characteristics are
different among individual sensors.
[0157] Therefore, in order to enhance the correction accuracy in
the signal processing unit 3, it is important to set an optimum
comparison threshold TH for each of the individual sensors.
[0158] In a comparison threshold setting method of the present
embodiment, when the flow advancing from upstream toward downstream
is defined as a forward flow and the flow advancing from downstream
toward upstream is defined as a reverse flow, the flow rate
characteristic on the reverse flow side of the sensor is measured,
and a flow rate signal that corresponds to a target flow rate is
set as the comparison threshold TH.
[0159] As an example, although the reverse flow characteristic of a
single sensor is different between a sensor 1 and a sensor 2 due to
influence of variation in the mounting state or the like as shown
in FIG. 11, if the reverse flow characteristic is measured for each
sensor, a target comparison threshold can be accurately
obtained.
[0160] As described above, according to the present embodiment, in
a thermal air flow meter including:
[0161] a bypass flow path which is disposed in an intake pipe in
which intake air to be taken into an internal combustion engine
flows and which takes in part of the intake air and causes the part
of the intake air to flow therethrough;
[0162] a sensor which has a flow rate detection element disposed in
the bypass flow path and which outputs an output signal that
corresponds to a flow rate of the intake air flowing in a forward
flow direction and a reverse flow direction in the intake pipe;
and
[0163] a signal processing unit which processes the output signal
of the sensor,
[0164] the signal processing unit includes: [0165] a response
correction unit which outputs a first amplitude-increased signal
and a second amplitude-increased signal which are each obtained by
subjecting the output signal of the sensor to an
amplitude-increasing process of an alternating current component
thereof; [0166] a comparison signal output unit which compares the
second amplitude-increased signal with a comparison threshold set
in advance, and which outputs a comparison signal on a negative
side that corresponds to a negative side portion, of the second
amplitude-increased signal, which is on the negative side with
respect to the comparison threshold; [0167] an averaging processing
unit which outputs an average signal obtained by averaging the
comparison signal; [0168] a coefficient multiplication processing
unit which outputs a coefficient-multiplied signal obtained by
multiplying the average signal by an adjustment coefficient set in
advance; and [0169] a signal correction processing unit which
outputs, as a flow rate signal, a value obtained by correcting the
first amplitude-increased signal so as to be decreased by use of
the coefficient-multiplied signal, and
[0170] the comparison threshold is set on the basis of a flow rate
characteristic of the reverse flow side of the sensor measured in
advance.
Second Embodiment
[0171] In the first embodiment, the comparison threshold TH is
calculated on the basis of the flow rate characteristic on the
reverse flow side of a sensor having been measured. However, as a
second embodiment, an example is described in which a comparison
threshold is calculated by use of values of an adjustment value and
the forward flow characteristic having been measured.
[0172] When a sensor is assembled, in adjustment of the forward
flow characteristic to attain a desired characteristic, a raw
output Dm of the sensor is corrected by use of a gain G and an
offset Doff as shown in Expression (6) below.
[0173] Here, Dm is a value obtained by subjecting a raw output Vm
of the sensor to A/D conversion.
Dout=G(Dm-Doff) (6)
[0174] The parameters that can be confirmed by an actual flow rate
characteristic test machine are an output Dout after correction,
the gain G, and the offset Doff. Thus, Dm is obtained by Expression
(6) for calculation of a comparison threshold TH. If the obtained
Dm is put into Expression (7) below, the comparison threshold TH
can be calculated.
TH=Dm(1)-K*(Dm(2)-Dm(1))/(Qm(2)-Qm(1)) (7)
[0175] Here, TH is the flow rate signal of the sensor that
corresponds to a comparison threshold, K* is a coefficient, Dm(1)
and Dm(2) are the flow rate signal at two points on the forward
flow side of the sensor, and Qm(1) and Qm(2) are flow rate values
that correspond to Dm(1) and Dm(2), respectively.
[0176] The variation of the comparison threshold TH of each sensor
when Expression (7) is used is obtained. FIG. 12 shows pulsation
error under the conditions of pulsations 1, 2 accompanied with
reverse flows, when the comparison thresholdTH is set at the upper
limit value, the median, and the lower limit value of the
variation.
[0177] In all cases where the comparison threshold TH is the upper
limit value, the median, and the lower limit value, the pulsation
error is at levels that are harmless in actual use
environments.
[0178] In addition, the second embodiment does not require
measurement of the reverse flow, and thus, is advantageous in that
no reverse flow measuring device is required, and that man-hour
during assembling can be reduced.
[0179] It is needless to say that, as the flow rate signal of the
sensor used in calculation of the comparison threshold TH, the
value before the A/D conversion can be used.
Third Embodiment
[0180] Even when a flow rate signal Dm(0) at a time of no air flow
of the sensor is used as Dm(2) in Expression (7) described in the
second embodiment, the comparison threshold TH can be accurately
obtained.
TH=Dm(0)-K*(Dm(1)-Dm(0))/Qm(1) (8)
[0181] Here, TH is the flow rate signal of the sensor that
corresponds to a comparison threshold, K* is a coefficient, Dm(1)
is the flow rate signal on the forward flow side of the sensor,
Dm(0) is the flow rate signal of the sensor at a time of no air
flow, and Qm(1) is a flow rate value that corresponds to Dm(1).
[0182] Also when the comparison threshold TH is calculated
according to the third embodiment, the variation of the comparison
threshold TH is at a level similar to that described in the second
embodiment, and the influence on the pulsation error is at a
harmless level.
[0183] Furthermore, the number of the points where a flow rate
characteristic test machine measures the flow rate can be reduced
by one compared with that in the second embodiment. Thus, man-hour
during assembling can be reduced.
[0184] It is noted that, within the scope of the present invention,
the above embodiments may be freely combined with each other, or
each of the above embodiments may be modified or abbreviated as
appropriate.
[0185] Various modifications and alterations of this invention will
be apparent to those skilled in the art without departing from the
scope and spirit of this invention, and it should be understood
that this is not limited to the illustrative embodiments set forth
herein.
* * * * *